The long-term goal of this research is to determine the distribution, metabolism and physiological roles of the essential trace element zinc in the crystalline lens, especially with respect to the maintenance of its transparency and the prevention of cataracts. Zinc is present in remarkably high concentrations in the eye, including the lens. It is present in many metalloenzymes reflecting its roles in nucleic acid and protein metabolism (and hence cell replication, growth and repair) especially in cutaneous tissues, which have an embryological kinship to the lens. Zinc also contributes to the stability of cell proteins and membranes, protecting them from damaging stimuli. A potential role for zinc in maintaining the integrity and transparency of the lens is apparent but very little is known about its distribution, metabolism, regulation or physiological roles in this tissue. Serum zinc concentrations decrease in a number of circumstances including old age, some dietary regimens, in several diseases, including diabetes mellitus and diarrheal disease, and the use of some drugs such as ethanol, oral contraceptives and thiazide diuretics. Some such conditions are known to result in a predisposition to cataracts in humans. Superoxide dismutase is a zinc metalloenzyme which is currently exciting considerable interest as it destroys superoxide radicals which are thought to contribute to oxidative damage which may initiate the formation of cataracts. Superoxide dismutase levels in the human lens decline in old age and in cataracts. Zinc concentrations in the human lens have also been observed to decrease in old age and in cataracts. It is proposed to study the effects of dietary zinc- deficiency and excess on the content, distribution and metabolism of zinc in the crystalline lens of adult and young developing rabbits. Zinc will be assayed by atomic absorption spectrophotometry and the use of the isotope zinc-65. The susceptability of lenses from such rabbits to damage by oxidative agents will be studied by, in vitro, by measuring changes in their permeability, using the isotope rubidium-86. The levels of superoxide dismutase will be measured in lenses from rabbits in different zinc nutritional statuses; normal, deficient and excess.